Psychotropic effects of caffeine in man. IV. Quantitative and qualitative differences associated with habituation to coffee

Caffeine (150 and 300 mg.) and placebo were administered in decaffeinated coffee on 9 successive mornings (each treatment 3 times) to 18 housewives who were not coffee drinkers and to 38 who habitually drank 5 cups or more daily. The design was blind. The criteria of caffeine effects were 11 clusters of adjectives on a self‐rating form, used at 30 minute intervals for 2 hours. Major differences between effects of caffeine on abstainers and on users were revealed. The abstainers felt quite normal when placebo was administered but reacted negatively to caffeine; principal complaints were jitteriness, nervousness, and "upset stomach." The users complained of sleepiness and also of dysphoric symptoms such as irritability when placebo was administered or before caffeine was administered. The users reacted positively to caffeine, reporting increased alertness, decreased irritability, and a feeling of contentedness. These findings are entirely consistent with those obtained by a questionnaire survey in the same and other women, reported in the preceding paper. The possible implications for understanding the genesis of drug‐seeking behavior in man are discussed.